APP and Alzheimer disease: In addition, presenilin, APP, C-terminal fragments of APP (APP-CTFs), and several key proteases in Aβ production such as β-secretase (BACE1) and γ-secretase (presenilin subunits PS1 or PS2) are also found in exosomes isolated from AD brain tissues (Perez-Gonzalez et al., 2012).